Patent Application
20080264231
Saw blades comprising a steel plate having a plurality of teeth formed on the plate are known. The teeth may comprise a tooth formed integrally with the plate with a tip is brazed onto each tooth. The conventional saw blade having a tip brazed onto each tooth, while relatively straight forward to manufacture, is less durable and has a shorter maximum life, especially in abusive situations such as nail strikes, than is desirable. Attempts to weld traditionally shaped tips onto the steel plate have resulted in cracking in the tip/plate interface due to stresses caused by the welding process. Further, in order to be cost effective, any process for attaching the tips to the plate must not require extensive subsequent processes to obtain the final tip geometry.
Thus, an improved saw blade tooth construction, saw blade and blade manufacturing process that allow the tip to be welded to the plate in a manner that provides a strong tip/plate interface and that is economical to manufacture is desired.
A saw blade comprises a plate having a plurality of teeth. Each of the teeth includes a tip where the tip has a smooth curved surface welded to the plate. The tip comprises a solid piece of hard material and has a generally rounded wedge shape. A method of forming a saw blade comprises providing a plate having pockets formed therein. A tip having a generally rounded wedge shape is welded to the plate.
Each tooth 2 consists of a tooth support 8 supporting cutting tip 10. Tooth support 8 may be formed integrally with the plate 4, and extends radially from the periphery of the plate 4. A gullet 14 may be formed between each of the teeth defining the areas between the teeth. In one embodiment cutting tip 10 is formed of a hard material such as tungsten carbide welded onto the tooth supports 8 at tip pockets 20. Tips 10 typically would be made of a material having a high hardness and would ordinarily be of a harder and more expensive material than plate 4 and tooth supports 8. In one embodiment the plate 4 is made of steel and the tips 10 are made of carbide.
The use of a resistance welded joint between the tip 10 and the plate 4 provides higher bond strength between the tips 10 and plate 4 when compared to a brazed joint and will result in longer blade life and better durability especially in abusive situations such as nail strikes. It has been determined, based on tests using traditional shaped and sized carbide tips welded onto the plate, that the welding of such tips results in cracking of the carbide caused by stresses imparted during the welding process and a lack of fusion at the joint due to a lack of electrical contact and a suitable concentrated electrical pathway between the tip and the plate.
To avoid these problems a tip having a particular geometry has been developed that reduces the internal stressing of the carbide tip and provides a desired current path during the welding process. The tip shape also minimizes the amount of excess material that must be removed subsequent to the welding process to obtain the final tip geometry.
Referring to
Each tooth support 8 comprises a pocket 20 for receiving the rounded portion 16a of tip 10. The pocket 20 may be arranged such that there is full contact between the pocket and rounded portion 16a as best shown in
To join a tip 10 to the pocket 20 a welding operation is used. A tip 10 shaped as disclosed herein is provided (block 901). A plate 4 having a tip pocket 20 is also provided (block 902). Tip 10 is positioned in the pocket 20 as described above such that the tip contacts the pocket (block 903). An electrode 25 contacts the opposite flat sides 16b and 16c of the tip (block 904) and typically a force is applied to the tip such that the tip 10 is held against the pocket 20 under pressure (block 905). The opposed flat side portions 16b and 16c ensure that good contact is achieved between the electrode 25 and the tip 10 both to create the pressure contact between the blade and the tip and to ensure good current flow between the electrode and the tip. Current is applied to the tip 10 via electrode 25 (block 906). Because the tip 10 is essentially symmetric from between the contact points 25a and 25b of the electrode 25 and rounded portion 16a, current flows evenly around rounded portion 16a and the contact point(s) with the pocket 20 such that an even resistance weld is made between the tip and the plate.
After the tip is welded to the plate, the tip is ground to create the final tip shape (block 907). Referring to
In one embodiment the tip 10 may be coated such as with a Nickel coating. The coating helps with the electrical contact between the tip and the electrode and also acts as a bonding aid in that it increases the metallurgical bond because it reacts with both the carbide tip 10 and steel plate 4 to create increased bond strength when compared to a non-coated tip. A coating such as a Nickel coating may also be used with the tips shown in
An alternate embodiment of the tip is shown in
Another embodiment of the tip is shown in
Specific embodiments of an invention are described herein. One of ordinary skill in the art will recognize that the invention has other applications in other environments. In fact, many embodiments and implementations are possible. The following claims are in no way intended to limit the scope of the invention to the specific embodiments described above.
