Isolated coastal rocks and beaches serve as haul-outs for harbor seals and California sea lions. Although Bay shores were once filled with pinnipeds, concentrations such as the hundreds of harbor seals that haul out in Point Bonita Cove at Marin Headlands can still be found.
Significant harbor seal pupping areas are found in Bolinas Lagoon and Tomales Bay. The northern elephant seal population has been rapidly increasing, leading to more encounters on sandy beaches throughout the region, including a fairly large colony at Point Reyes National Seashore. California gray whales, humpback whales, and harbor porpoises use nearshore waters.
Young whales occasionally wander into San Francisco Bay. Southern sea otters are infrequently seen offshore with numbers increasing as the population spreads north from Monterey Bay.
Browse articles and information summaries about mammals at Golden Gate. Where do mammals live in Golden Gate? Explore the natural features and ecosystems that mammals and other organisms call home. Explore This Park. Lastly, whether you have a cold sprue or a hot sprue bushing, add a 0. In order to discuss edge gates, we need to first discuss land length.
The land length for an edge gate is a short straight section connecting the outer surface of the part to the runner, as shown in Fig. Longer lands impart more shear to the material, which in turn reduces the material viscosity. That can be beneficial, if not necessary, to help improve the flow length into the cavity. Long land lengths can also be detrimental and create burns with shear-sensitive materials, such as PVC.
The longer the land length, the greater the pressure required to push the material through the gate—like breathing through a long straw versus a short straw. However, since long lands reduce the viscosity of the material, it takes less pressure to fill the cavities—especially at high injection velocities.
There is an old rule of thumb that says the gate land length should be half the depth of the gate. Both worked just fine for their particular application.
Your decision on how long to make the gate land should be based on the expected injection velocity. If you are going to inject extremely fast, such as with a thin-walled part having a shallow gate depth, a short land length is usually necessary. If you are going to inject extremely slowly, such as with a thick-walled part having a very deep gate, the land length can be considerably longer, because there is very little pressure loss going through that gate. The ideal land length is also somewhat material dependent.
It is always best to start with a slightly longer gate land. If there is an issue with either high shear or high injection pressure going through the gate, it is steel-safe and you can reduce it.
The resulting processing window will be narrow and the likelihood of rejects will increase exponentially. Whatever you do, just make sure all of the gates in a multi-cavity mold have the exact same gate depth, width and land length. Otherwise, you will get a cavity imbalance. In May , Bill Fierens now s r. Holland Co. I spoke with both authors, and while there is no empirical data to support this statement, we all believe it to be true for two primary reasons.
First, short lands have less steel in the gate area, and area is a primary variable in the mathematical equation for calculating the rate of heat transfer by conduction. Second, the shorter the land length, the closer the runner is to the gate—putting additional heat into this critical area.
Additionally, if the wall of the molded part is thick, it also puts additional heat into the critical area. As mentioned before, thick-walled parts or parts with large round runners can require longer lands.
While I am certain that a gate with a 1-in. Additionally, since shorter lands develop less shear, there will be less temperature rise in both the material and the steel. Without empirical data, we will never know for sure.
This brings up another point worth mentioning. Companies that have adopted scientific molding methods perform gate-freeze studies on their molds. Basically, you start with a very short second-stage hold time—about 1 sec, and then weigh the part s.
You then incrementally increase the hold time while maintaining the cycle time, until the part weight no longer increases. But all was not as it seemed. Our vet at the time, Dr. Bob Braun, was able to get a good look at RK30 during the encounter and positively confirmed that she had been entangled. However, Dr. Braun realized that RK30 didn't have a piece of line around her after all, just a permanent indentation created from a lengthy past entanglement.
At some point in her life, RK30 had freed herself of an entanglement, but it took a while for her to shake loose of the line as evidenced by the remaining, dramatic scar around her neck.
RK30 had, luckily, slipped her noose before the entanglement could kill her. She also has boat propeller scars on her belly and a large scar on her left side, probably from an encounter with a large shark.
Unfortunately, not all of RK30's offspring have survived. One pup, when it was very young, got washed out to sea by heavy surf.
Another died after ingesting a fishing hook.
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