BARREL FOR A TIMEPIECE

Description

Technical field of the invention

[0001] The present invention relates to a timepiece and is particularly directed to a mechanical timepiece wherein the barrel is made of titanium and/or titanium alloy in order to produce a lighter weight barrel. The mating wall surface of the barrel is of oxidized titanium surface. The oxidation process is achieved through plasma electrolytic oxidation or microarc oxidation. The oxidised titanium surface of the barrel provides less frictions between the mating wall surface of the barrel and the main spring, thereby increasing the accuracy rate and reducing energy loss.

Background of the invention

[0002] In a mechanical timepiece, the drive power is provided by a main spring by being transmitted to the barrel. Thereby, the main spring is fitted in the barrel and freely engages the inner surface of the barrel wall. It is possible to rivet the outer end of the main spring to a friction spring. This friction spring together with the wall of the barrel forms a slip coupling which prevents over-winding of the main spring by allowing the outer end of the main spring to slip when it is being wound.

[0003] It is generally known that the frequent and repetitive frictional movement between the main spring and the inner wall of the barrel of the timepiece results in an inaccurate rate and functioning of the watch after a relatively short period of time. Due to the repetitive frictional movement between the mating surface of the main spring and the mating surface of the barrel, a large proportion of energy is lost during the frictional process. It is estimated that at least forty relative frictional movements per day between the main spring and the barrel occur. This corresponds to more than 14,600 frictional movements in a year, thereby affecting the accuracy of the timepiece.

[0004] Numerous attempts have been made to overcome energy loss through the frictional movement between the main spring and the inner wall of the barrel. It is generally believe that the energy loss can be prevented if the barrier material is softer than the spring material, as it was believed that the softer barrel material would "give", thus avoiding wear and unnecessary energy loss.

[0005] For these reasons, timepiece barrels are typically made of brass while the main spring is made of steel. As the steel is harder than brass, it was generally accepted that this combination of mating materials favourable reduces wear and energy loss. To obtain a still softer mating surface, gold or a layer of high quality synthetic material has been used to plate between the outermost turn of the spring and the inner wall of the brass surface of the barrel.

[0006] However, there remains a need in the art to provide an alternative to produce timepiece barrel that has a lighter weight, has a higher strength, is corrosion-protective, is efficient in transferring energy by minimising frictions, low cost and is abundant and can be found easily.

Detailed disclosure of the invention

[0007] The inventors of the present invention have surprisingly found out that the above-formulated need can be met by using titanium in producing timepiece barrel. Titanium is abundant on the sub-surface of the earth and can easily be found. Titanium could be mixed with other metal elements, forming titanium alloy. Such alloys have very high tensile strength and toughness (even at extreme temperatures). There are light in weight, have extraordinary corrosion resistance and the ability to withstand extreme temperatures.

[0008] The barrel is furthermore treated with plasma electrolytic oxidation or microarc oxidation to achieve a satisfying oxidized titanium on the mating surface of the timepiece barrel. Barrel made of titanium not only gives a light weight and thereby reduces the overall weight of the timepiece, the oxidation process through plasma electrolytic oxidation or microarc oxidation renders less energy loss as fewer frictions occur between the mating surface of the surface wall of the barrel and the mating surface of the main spring, and hence increases its accuracy rate. Furthermore, another advantage of using titanium in producing barrel is of its high strength-to-weight ratio compared to other typically used materials such as brass.

[0009] Therefore, in a first aspect, the present invention relates to a timepiece having a barrel, wherein a main spring is located within the barrel, wherein the hardness of the material of the main spring is substantially equal or higher than the hardness of the material of the mating wall surface of the barrel, wherein the material of the mating wall surface of the barrel comprises titanium. The titanium barrel has a lighter weight compared to other conventional timepiece barrel, for instance barrel made of brass. The titanium barrel also has the hardness equal or less than the main spring, thereby "give" to avoid energy loss due to frictions between the mating surface of the timepiece barrel and the main spring.

[0010] In one preferred embodiment of the present invention, the material of the mating wall surface of the barrel is titanium alloy Grade 5. Titanium alloy Grade 5 also known as Ti6Al4V, Ti-6Al-4V or Ti 6-4. The chemical composition of the titanium alloy Grade 5 comprises of 6 % aluminium, 4 % vanadium, 0.25 % (maximum) iron, 0.2 % (maximum) oxygen, and the remainder being titanium. It is significantly stronger than commercially pure titanium while having the same stiffness and thermal properties (excluding thermal conductivity). Titanium alloy Grade 5 is especially known for its heat treatable properties. For these reasons, this grade is an excellent combination of strength, corrosion resistance, weld and fabricability and thereby is chosen as an alternative material for timepiece barrel according to the present invention.

[0011] In another preferred embodiment of the present invention, the mating wall surface of the barrel is of oxidised titanium surface. The oxidised titanium barrel generally gives a dark grey corrosion-protective layer to prevent the corrosion of the barrel. The oxidized titanium surface of the barrel according to the present invention has improved wear and corrosion resistance as well as anti-galling properties. In this connection, the oxidised titanium barrel renders less energy loss resulting from frictions between the mating surface of the titanium barrel and mating surface of the main spring.

[0012] The oxidized titanium surface of the mating wall surface of the barrel according to one specific embodiment of the present invention may be of AMS 2488C standard, which is anodic treated. Anodization process accelerates the formation of an oxide coating under controlled conditions to provide the desired result. Titanium anodizing provides the advantages of hardening and colouring the surface of titanium components without altering the surface properties of the metal. By precisely specifying the surface oxide level, an entire range of colours can be produced. The resulting anodize colours are achieved without any dyes or coatings, therefore the surface properties remain unchanged, making the part suitable for different applications including in timepiece.

[0013] The titanium anodizing process combined with passivation produces implant grade cleanliness, while the resulting colours provide for product identification. The process also improves the fatigue strength of the titanium, with minimal dimensional change. Although titanium anodizing is primarily used in the medical industry, there is an increasing interest in the consumer, especially in the luxury markets such as timepiece. Titanium colour anodizing has many advantages including large colour spectrum, produces a clean and passive surface. On another hand, titanium type II anodizing has the advantages such as anti-galling, lubrication, increased resistance to galvanic corrosion and has a passive surface.

[0014] Therefore, in one further preferred embodiment of the present invention, the mating wall surface of the barrel is treated with plasma electrolytic oxidation or microarc oxidation thus giving the oxidised titanium barrel which has the corrosion-protective effect as well as efficient in transferring energy from main spring to the barrel by avoiding unnecessary energy loss by reducing friction rate.

[0015] In yet a further embodiment according to the present invention, the main spring is made of metal or non-metal. Non-metal main spring may comprise of silicon or fibre enhanced plastic such as fibreglass. These non-metal materials are suitable to make main spring. As the matter of fact, non-metal main spring has advantages over metal main spring for instance the increased torque and also its efficient in storing energy. Furthermore, main spring made of silicon or fibre glass loses less than 1 % energy compared to metal main spring which could lose more than 10 % energy in a period of 24 hours.

[0016] Nonetheless, metal main spring such as steel or any metal that has a relatively high hardness are widely used to make main spring due to its economic value as well as its easy and simple construction. The main spring which is made of steel, although not optimal, could also efficiently transfer its power to the barrel.

[0017] In a yet further embodiment according to the present invention, the metal main spring is made of alloy, preferably on Ni-Co-Cr basis. The alloy main spring has a higher strength compared to steel main spring and it is resistant to corrosion.

[0018] Therefore, in order to overcome the above-described drawbacks of the presently available brass barrel, present invention searches for alternative composition to produce a barrel that is lighter and in the meantime which is more efficient is transferring energy while minimizing frictions which is the major reason contributing for energy loss. The inventors of the present invention discovered that barrel which is made of titanium renders the weight of the barrel significantly less than the barrel that is made of brass by approximately 10 % or up to 40 %.

[0019] Furthermore, titanium barrel surface that is treated with oxidation process such as plasma electrolytic oxidation or microarc oxidation renders less friction between the mating surface of the barrel and the mating surface of the main spring, while the oxidized titanium surface of the barrel acts as a superior corrosion-protective layer.

[0020] In one example of the embodiment of the present invention, the mating wall surface of the barrel is made of titanium and/or titanium alloy according to the present invention whereas the non-mating wall surface of the barrel (for instance the outer and bottom wall surface of the barrel) maybe made of other conventional metal elements, for instance of brass. As aforementioned, only the mating wall surface of the barrel which is in exposed to the movements of the main spring plays a critical role in reducing the frictional rates thereby losing the transmitted energy from the main spring to the barrel. Barrel having a combination of brass or any other metals and titanium according to the present invention provides a superior combination, whereby on one hand, less friction on the mating wall surface occurs thus less energy is lost, on another hand, an ideal weight of the timepiece can be regulated through the barrel while the cost of the barrel can be kept at an optimal level. For this reason, different timepiece weights accustomed to different purposes or users (male, female or children timepiece) can be produced accordingly.

[0021] By "about" or "approximately" in relation to a given numerical value for amount or weight, it is meant to include numerical values within 10% of the specified value.

[0022] By "comprising" it is meant including, but not limited to, whatever follows the word "comprising". Thus, use of the term "comprising" indicates that the listed elements are required or mandatory, but that other elements are optional and may or may not be present. The terms "comprising" and "including" as used herein are interchangeable with each other.

[0023] By "consisting of" is meant including, and limited to, whatever follows the phrase "consisting of". Thus, the phrase "consisting of" indicates that the listed elements are required or mandatory, and that no other elements may be present.

[0024] The indefinite article "a" or "an" does not exclude a plurality, thus should be treated broadly.

[0025] The invention has been described broadly and generically herein. Each of the narrower species and sub-generic groupings falling within the generic disclosure also form part of the invention. This includes the generic description of the invention with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein.

[0026] Other embodiments are within the following claims and non-limiting examples. It is to be understood that these examples are for illustrative purposes only and are not to be construed to limit the scope of the present invention.

Claims

1. A timepiece having a barrel, wherein a main spring is located within the barrel, characterised in that the hardness of the material of the main spring is substantially equal or higher than the hardness of the material of the mating wall surface of the barrel, wherein material of the mating wall surface of the barrel comprising titanium.

2. The timepiece according to claim 1, wherein the material of the mating wall surface of the barrel is titanium alloy Grade 5.

3. The timepiece according to claim 1 or claim 2, wherein the mating wall surface of the barrel is an oxidised titanium surface.

4. The timepiece according to anyone of the preceding claims, wherein the mating wall surface of the barrel is treated with plasma electrolytic oxidation or microarc oxidation.

5. The timepiece according to claim 3 or claim 4, wherein the oxidized titanium surface of the mating wall surface of the barrel is of AMS 2488C standard.

6. The timepiece according to anyone of the preceding claims, wherein the main spring is made of metal or non-metal.

7. The timepiece according to claim 6, wherein the non-metal main spring comprising silicon and/or fibre reinforced plastic.

8. The timepiece according to claim 6, wherein the metal main spring is made of steel.

9. The timepiece according to claim 6, wherein the metal main spring is made of alloy.

10. The timepiece according to claim 9, wherein the alloy of the metal main spring is on Ni-Co-Cr basis.